<!DOCTYPE html>
<html lang="en" style="font-size:100px">

    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>Document</title>
    </head>
    <style>
        .a1 {
            /* font-size: 20px; */
            width: 10em;
            background: #fcc;
        }
        .a2{
            /* font-size: 40px; */
        }
    </style>

    <body>
        <div class="a2">
            <div class="a1">
                我是牛逼的内容
            </div>
        </div>

    </body>

</html>